It is highly desirable to be able to minimize the amount of service required for internal combustion engines to thereby minimize the interruption in the use of the vehicle/equipment. Degradation and contamination of engine lubricating oil during engine use requires oil changing procedures which account for a significant portion of the maintenance and associated engine "down time". Conventional periodic oil changes generate an accumulation of waste lubricating oil which must be disposed of and/or processed resulting in undesirable costs. Therefore, extending oil drain intervals and reducing waste disposal are of great value to vehicle/equipment operators.
Consequently, systems have been developed for automatically changing internal combustion engine crankcase oil during engine operation. For example, U.S. Pat. No. 3,447,636 discloses a system for automatically changing engine oil while the engine is operating. The system operates to drain substantially all of the used oil from the engine immediately prior to introducing fresh oil into the engine from a reservoir. The single operation process results in a complete change of the substantially the entire engine oil volume. However, draining the engine prior to refilling with fresh oil necessarily creates a risk that an inadequate supply of lube oil exists in the engine for an interim time period possibly resulting in damage or excessive wear to engine components from insufficient lubrication. Moreover, this system undesirably results in a quantity of waste oil.
Other systems have been developed which automatically change engine lube oil during engine operation while avoiding a waste quantity of oil by directing the used lube oil into the fuel system for burning with the fuel in the engine. These systems periodically drain a small amount of the used oil from the engine lube oil system, and replace the drained quantity with fresh lubricant from an auxiliary tank. For example, U.S. Pat. Nos. 4,869,346 and 5,390,762 to Nelson disclose an automatic crankcase oil change and makeup system including a displacement unit having a piston with a predetermined stroke set to deliver identical, predetermined amounts of fresh oil during each stroke at the same flow rate and volume as the extraction of used oil. The frequency of the pressure strokes is set by a timer in an electronic controller, and is adjustably set to stroke at fixed time intervals to provide a cumulative quantity of fresh oil to the crankcase according to the regular recommended oil change period for the particular engine. A pair of dials on the controller enable the frequency of the pressure strokes to be adjusted. U.S. Pat. Nos. 4,421,078; 4,495,909; and 5,431,138 to Hurner disclose similar systems for oil changing and making up during engine operation which include a control module having an adjustable impulse timer set to periodically cycle an air pressure operated oil extractor pump at a fixed time intervals to direct a predetermined amount of engine oil out of the oil pan and into the fuel tank. Fresh makeup oil is pumped from an oil reservoir to the crankcase, also by air pressure, in response to a low level signal from a dipstick sensor. Similarly, U.S. Pat. No. 4,417,561 to Yasuhara discloses an automatic oil changing and disposing apparatus wherein used crankcase oil is periodically directed to a fuel tank via a valve controlled by an odometer switch, and fresh oil is gravity fed from a fresh oil tank to the crankcase via a control valve controlled by a crankcase oil level switch. The quantity of each increment of used oil removed from the crankcase, and each increment of fresh oil supplied, is controlled by respective timers having variable on-time duration to effect variable control of engine oil extraction and addition.
Although capable of automatically changing lube oil during engine operation, the automatic oil changing systems discussed hereinabove are incapable of accurately varying and controlling oil changing in response to the actual needs of the engine that vary based on the engine operating conditions, such as fuel consumption. The amount of oil drained from the crankcase and injected into the fuel system is often either less than the necessary replacement rate when the engine is being used more heavily than expected, or more than the optimum amount when the engine is being used less heavily than expected. Injecting too little used oil from the oil sump into the fuel system will disadvantageously result in engine damage from over-used oil incapable of adequately lubricating and cooling engine components. On the other hand, injecting too much oil results in excessive concentrations of used oil in the fuel resulting in engine performance degradation, increased emissions, shortened fuel filter life and wasted oil. In addition, if the engine is a recent emission regulated engine, injecting too much oil into the fuel system will result in emission non-compliance and possibly a fine. Although Yasuhara '561 suggests variable control of engine oil extraction and addition, this reference does not suggest means for accomplishing such variable control nor the engine operating parameters to be considered. The Nelson '346 and '762 references only suggest varying the amount of oil extracted and added to the engine crankcase by manually adjusting timers to vary the frequency of oil additions and extractions.
British application No. 867,711 discloses a system for creating a controlled injection of engine lubricating oil into the engine's fuel system. The amount of oil added to the fuel system may be controlled in dependence on engine load in a first embodiment or engine speed in a second embodiment. In both embodiments, oil is injected into the fuel system via a groove formed in a fuel injection pump plunger. In the first embodiment, the annular groove is shaped with a varying cross-section. The plunger is rotated based on engine load to vary the flow area of the groove thereby varying the amount of injected oil. In the second embodiment, oil injection is controlled based on engine speed by varying the oil pressure in the suction chamber. A fuel passage containing a throttle orifice connects the fuel supply pump to the suction chamber. As the volume of fuel injected increases, the pressure in the suction chamber decreases which draws a larger quantity of oil into the chamber. However, each embodiment of this system is incapable of controlling oil injection based on more than one engine condition. As a result, each embodiment of this system is incapable of effectively varying the rate of oil injection to maintain the proper quality of lube oil in the sump while also ensuring an acceptable concentration of oil in the fuel. In addition, this system does not provide an automatic means for replacing the engine's oil sump. Also, since this system requires modifications to an engine's fuel pump, this system may not be easily retrofit on existing engines.
U.S. Pat. No. 4,674,456 to Merritt discloses a system for effecting periodic partial replacement of used oil with fresh oil. A first container holds fresh oil, a second container holds used oil, and separate respective pumps transfer fresh oil to the engine and remove used oil. In operation, fresh oil approximating the total capacity of the crankcase or oil reservoir is poured into the first container. In the example provided by Merritt, if the manufacturer recommends that five quarts of oil be replaced every 3000 miles, the system is programmed to remove one quart of used oil after 600 miles. The controlling means senses the engine running time or the miles driven and activates the respective pumps at each running time or mileage interval. Fresh oil is added at a substantially equal rate to the rate of oil removal from the crankcase to maintain a constant amount of oil within the oil reservoir of the engine. The controlling means may receive a modifying input signal from a thermocouple measuring engine temperature to increase the rate of oil replacement if above-average engine temperature is measured. However, varying the amount of predetermined oil replacement based merely on variations in the engine operating temperature does not result in the optimum lube quality throughout engine operation. Moreover, this system does not provide any means for compensating for oil burned in, or inadvertently leaked from, the engine. In addition, this system does not direct used oil into the engine' fuel system and, therefore, undesirably results in a quantity of waste oil which must be disposed of or processed.
U.S. Pat. No. 4,506,337 to Yasuhara is noted for disclosing an engine lube oil replacement timing monitoring system comprising a microcomputer which calculates the amount of soot suspended in the lube oil on the basis of engine speed and engine load whereby the expired life of the engine oil can be accurately detected so as to permit oil changing. The microcomputer operates an indicator alerting the operator of the need to change the oil. Thus, instead of automatically changing the oil during engine operation, this system disadvantageously requires the engine to be shut down prior to changing the oil and inevitably produces a quantity of waste oil which must be disposed of. In addition, this system fails to consider other critical engine operating conditions and parameters and, therefore, does not determine the optimum time interval between oil changes nor maintain the quality of the oil at an optimum level throughout engine operation.
Therefore, there is a need for a continuous engine lube oil replacement system capable of more effectively controlling the quantity of used lube oil burned in the engine based on varying engine operating conditions.